I have been a conrad-johnson fan ever since I purchased a tubed PV-10A preamplifier somewhere around 1990. OK, since I've never owned a PV-5 some might consider me a Johnny-come-lately, but still, ever since then I have had more than a few positive experiences with a number of their solid-state and tubed preamplifiers and power amplifiers. In general, what I've discovered is that C-J products have a midrange to die for (well, or at least within risk of doing so, since no audio product is worth that kind of sacrifice), and a very lifelike and musical character. But in their products from the early 1990s I sensed a hint of a burnished euphonic "golden glow" throughout their frequency range, especially in their more affordable components. In more recent times that slight patina has evaporated, and has been replaced by an ultra-transparent sound that manages to embrace the best of solid-state and tube worlds, regardless if they were designed with glass bottles or transistors. Even though there are sonic nuances between C-J's solid-state and tube units, they all maintain a lifelike, musical personality that always serves at the pleasure of the source. This is especially true when one considers their more ambitious products such as their ACT2 series of preamplifiers, components that should be regarded by all who have ears as state-of-the-art. Even their current line-up's less expensive solid-state "integrated", the CA-200 control amplifier has a sound that approaches a near ideal mix of the best of the solid-state and tubed attributes (see Todd Warnke's March 2007 review). In view of that, it is surprising that conrad-johnson proclaims in their advertising campaign that the ET250S hybrid power amplifier's tubed input stage supplies "harmonic character" whilst it's solid-state output stage "produces the muscle". If only other things in life were so simple. Are conrad-johnson's solid-state amps deficient in harmonic character? Do conrad-johnson's tube amps lack muscle? In both cases, absolutely not.
The ET250S is built with a zero feedback design that conrad-johnson says is judiciously employed to allow for, among other benefits, finer the gradations of microdynamics and to accurately reproduce the decay on musical transients. They go on to say that while increasing negative feedback decreases distortion, their careful design of the circuits, high parts quality, and their power supply design make zero feedback design achievable. The solid-state output stage of the ET250S uses what conrad-johnson claims are high-current bi-polar devices that have been selected for their extremely low output impedance and their ability to handle a great deal of current. C-J also claims that the "oversized" power transformers, "massive" power storage reservoirs with high-speed capacitor shunts that are largely responsible for the amp's excellent transient response. In their circuits they also feature, among other things, high-quality internal wiring, polypropylene, polystyrene and Teflon capacitors, except in the main power supply storage where high-speed electrolytics are used because of the extremely high capacitance required.
I could easily use Enjoy the Music.com's entire server space filling this review with all sorts of audiophile hyperbole regarding the ET250's wonderful sound, or lack thereof. Basically, it had all the neutrality and musicality as one should expect from an amp in its price range (and quite beyond). The hybrid C-J did not have the brilliantly sharp transient response that some lesser pure solid-state amps posses, and conversely, it did not sound at all sluggish as some lesser pure tube amps might have. So, did the conrad-johnson ET250S sound as if it was powered by a combination of both tubes and transistors? Yes and no, and I mean that only in the most positive of ways. I have much respect for Drs. Conrad and Johnson, and I assume that they know how to get the best out of both valve and solid-state circuits. So, I wouldn't classify the sound of the ET250s as having an abundance of tube warmth or solid-state snap, but appropriate degrees of both. And as I said, contrary to the simplistic description of the sound of the ET250S that conrad-johnson claims in their ad, neither its vacuum tube nor solid-state character called attention to itself. Again, I mean that in a positive way.
On Claudio Abbado's reading of Mahler's Seventh Symphony on DG, it was as if I was looking though a transparent sonic window at the Berlin Philharmonic laid out before me. I realize that not everyone is as taken as I am when it comes to Mahler symphonies, but that hardly matters when objectively listening to the reproduction of the orchestra going full tilt, or as Mahler is wont to do, when he reduces the orchestra to quadruple pianissimo for short moments during several passages. The amplifier's midrange was extremely neutral and silky smooth to boot, as was the entire extent of its high and low frequencies. Added to this was that I could seem to hear every iota of the decay of the hall sound. This piece showed the prowess of both the amp's macro- and micro-dynamic capabilities as well as its excellent transient response. Tympani whacks during the 3rd movement's cartoonish waltz were excellently reproduced, with the sound of the mallets striking the skins, the midrange resonance of the drum, and its room-shaking low-end heft. When the piece quickly shifted to the quiet portions of the movement, every instrument's subtle shadings were clearly audible.
The ET250S' neutrality, and by implication, its transparency, was on display in full measure when I compared two different pressing on two different formats of Yes' Fragile album — the CD re-issue on Mobile Fidelity and the Analogue Production's reissue on heavy vinyl. Given its vintage, both sounded as good as a multi-tracked recording could, and I assume both were produced from the original master tape. But it was easy to hear that the Mobile Fidelity CD dug deeper into the signal that was present on the original tape. Those who know me would assume that I would prefer the LP pressing, and it should be quite surprising that I preferred the CD given that the analog front end costs about ten times as much as the digital rig. But the amp's high level of transparency made it easy to hear that even though both formats had a midrange that was unexpectedly similar, the mids were more articulate on the CD without sounding too forward (rock ‘n' roll forward — yes, CD glare forward — no). Even though the LP had a typically pleasant analog-like warmth, on the CD Jon Anderson's vocals were more intelligible, yet at the same time better integrated into the song's complex structure. Also, the ET250S' powerful bass was on full display here, and showed the CD's low-end went significantly deeper and was more powerful than the LP. Chris Squire's Rickenbacker bass guitar and Bill Bruford's kick drum shook the window frames of the listening room.
Of course the ET250S' soundstaging prowess is definitely worth mentioning. Whether it is because tubes are in the signal path or just because the amplifier is simply designed correctly, the ET250S is a soundstage champion. But what I do not want to infer is that the amp generates an overblown soundstage via tube euphony. When the recording was up to it the soundstage was naturally stretched across the horizontal span of the speakers, creating a believable soundstage that was drawn to scale. Instruments and groups of instruments were placed in their proper location within this ‘stage, extending well behind and to the sides of the speakers when appropriate. I feel uncomfortable talking about "imaging", since a more accurate term would be instrument "placement" within the soundstage. It was simply a reproduction of what was captured by the microphones during the original event.
When I started writing this review, I told myself I was going to try and steer away from the cliché that the amp was a perfect blending of the attributes of tubes and solid-state. But I have to eat my words, and not only because the ET250S displayed the positives and did away with the negatives of both. Great solid-state amps have no problem sorting out complex passages, and so should great tube amps — but what the ET250S goes one further is by increasing what I like to call "dynamic distance" between instruments – when the amplitude of two or more simultaneously played instruments are different, and the component accurately displays this difference. The ET250S has the tautness and macrodynamic slam with plenty of power to spare; and microdynamic shadings that give life to the music. Of course no amp is perfect, so I am forced to mention that the amp's soundstage perspective was as if one's listening seat was a bit as if in Row M rather than the perfect Row H. I felt as if I was placed just a little further back in the hall than I'd like. The other criticism is that the amp only has unbalanced RCA inputs. Deal with it.